Thermoelectric devices, namely thermoelectric power generators and coolers, have emerged as promising green technology. In general, thermoelectric devices offer the ability to convert waste-heat energy into electrical power or provide cooling from a solid state device. Applications of thermoelectric devices range from electronic thermal management to solid state refrigeration to power generation from waste heat sources. The figure-of-merit (ZT) of a thermoelectric material is a dimensionless unit that is used to compare the efficiencies of various materials. The figure-of-merit (ZT) is determined by three physical parameters, namely, thermopower α (also known as a Seebeck coefficient), electrical conductivity σ, thermal conductivity k, and absolute temperature T.
  ZT  =                              α          2                ⁢        σ            k        ⁢          T      .      
Maximum ZT in bulk thermoelectric materials is governed by the intrinsic properties of the material system. Most candidates require low thermal conductivity as the driving force for enhanced ZT because of the inverse relationship between the Seebeck coefficient and electrical conductivity. This interdependence and coupling between the Seebeck coefficient and the electrical conductivity have made it difficult to increase ZT>1, despite nearly five decades of research.
While the intrinsic properties of the thermoelectric material are the primary factors that drive the efficiency of a thermoelectric device, performance is also limited by both parasitic electrical and thermal resistances present in the thermoelectric device. The parasitic electrical resistance is primarily due to a barrier to current flow that forms when an external metal electrode is applied to the surface of the thermoelectric material. A barrier formed at the metal-thermoelectric interface (which is a metal-semiconductor interface) introduces resistance that is detrimental to the performance of the thermoelectric device. The ideal ohmic contact to a semiconductor material follows the relationship:
            ρ      c        =                            ∂          V                          ∂          J                    ⁢              ❘                  V          =          0                    ⁢              Ω        ·                  cm          2                      ,where ρc is a contact resistivity of the ohmic contact, J is current density, and V is voltage. Low contact resistivity increases the performance of devices especially with thermoelectric leg dimensions in the range of 0.01 to 1 Millimeters (mm), and even more so with thermoelectric leg dimensions in the range of 0.01 to 0.5 mm where parasitic losses from the ohmic contacts become a major limit to the performance.
The thermoelectric material is generally a semiconductor, and the ohmic contact is generally a metal. In this case, one of the primary causes of high resistivity at the metal-semiconductor interface is a potential barrier that restricts the flow of charge carriers across the metal-semiconductor interface. It is thus important to select an ohmic contact metal that is a very close match in work function to the semiconductor such that the barrier height is small, in the range of 0.0 to 0.5 Volts (V) and preferably in the range of 0.0 to 0.3V.
Current thermoelectric devices have ohmic contacts with a contact resistivity in the range of 1×10−6 ohms-centimeter2 (Ω*cm)2 or above. This resistivity leads to losses in performance that become severe as the size of the thermoelectric legs in the device is reduced.
A further desirable feature of an ohmic contact to a thermoelectric material is a strong adhesive force between the metal and semiconductor surface. When the adhesive force between the metal and semiconductor surface is not sufficiently high, the device may be inoperable or fail earlier than desired. Many combinations of metal and semiconductor, which would be desirable because they would form an ohmic contact with low resistivity, do not have a sufficiently high the adhesive force between them.
As such, there is a need for systems and methods for increasing the adhesive force between a semiconductor material layer and an ohmic contact metal layer to provide a low resistivity ohmic contact.